PROJECT SUMMARY While environmental health disparities are known to be related to neighborhood-scale gradients in ambient exposures, housing attributes and in-home activities can further differentiate exposures along significant within- neighborhood socioeconomic gradients. Importantly, housing factors may not only modify personal exposures, but may also be a direct stressor with independent effects on health. Despite their importance in determining personal exposures to chemical and non-chemical stressors, household-level factors are rarely incorporated into epidemiological studies or risk analyses, leaving an important gap in evaluations of environmental health disparities. The goal for this project is to develop and implement innovative methods to provide improved estimates for between-household variability in exposures. We will identify the key determinants (among activity patterns, temperature, source usage, ambient pollutant concentrations, and air exchange rates) of indoor exposure to chemical stressors (e.g., PM2.5, ultrafine particles, NO2) within small spatial scales, to best characterize drivers of exposure disparities and to directly inform targets for future mitigation at the household level. In addition, we will characterize variability in non-chemical stressors (noise, thermal comfort) to understand the distribution of these key modifiers and their sociodemographic and structural predictors. We will focus our intensive exposure monitoring study on 200 homes in the Center?s two target communities of Chelsea and Dorchester, Massachusetts. We aim to determine how resident behavior and housing characteristics affect indoor-outdoor associations of chemical stressors, noise, and thermal comfort in our study population, considering the extent to which associations can be predicted by detailed individual activity data, more general questionnaire information, and publicly-available geospatial covariates. Finally, we will use community-based crowdsourcing approaches to assess housing and household characteristics to develop season-specific determinants that predict ventilation characteristics for every residence in Chelsea and Dorchester. Project 2 will involve close collaboration with community partners in the research and outreach/dissemination process through the Community Engagement Core, strengthening both the quality of the research and its potential to improve public health. These goals have direct linkages to the Center?s activities under Projects 1 and 3. Our results will contribute directly to the exposure disparities analyses and cumulative risk assessment applications in Project 3, and will help in the development of housing-related covariates to be tested in epidemiological studies within Project 1. We will also be able to identify intervention targets that have the greatest potential to reduce indoor exposures for those experiencing differential exposures to chemical and non-chemical stressors at home.